1. Field of the Invention
The present invention relates to a technique for performing printing by recording ink dots on a recording medium while a print head is moving in the main scan direction.
2. Description of the Related Art
Ink jet printers which eject ink from a head and laser printers have become popular as output devices for computers. Especially in recent years, color printers using color inks have also been widely utilized.
Various types of printing media for ink jet printers have been commercially marketed. Since the coloring properties of inks differ in different printing media, there are considerable differences in the images obtained. The type of printing medium used also affects the precision of the sub-scan feed of the printing medium (hereafter referred to as the xe2x80x9cpaper feedxe2x80x9d). For example, the actual feed amount may vary considerably between printing media with easy-slip surfaces and printing media with surfaces that do not slip easily, even if the same feed operation is performed. Furthermore, the precision of the paper feed tends to vary considerably from printer to printer.
The degree of precision of the paper feed has a great effect on the image quality. However, in the case of printers that perform printing using a so-called interlace recording mode, the image quality degradation caused by paper feed error can be suppressed to some extent by appropriately setting the paper feed amount. Here, the term xe2x80x9cinterlace recording modexe2x80x9d refers to a printing method that is performed using a print head that has nozzles aligned in a row at a nozzle pitch that is twice the dot pitch in the sub-scan direction (i.e., the main scan line pitch) or greater. In cases where such a print head is used, gaps are generated between the main scan lines (raster lines) that are recorded by a single main scan pass. Furthermore, a number of main scan passes that is equal to the number of main scan lines contained in these gaps is further required in order to eliminate the gaps. It is known that various feed amounts can be used in the case of such an interlace recording mode. Conventionally, therefore, the effect of variation in the paper feed precision on the mage quality has be minimized by appropriately selecting the paper feed amount in the interlace recording mode.
For the reasons described above, the direct correction of paper feed error in printers using an interlace recording mode has not been seriously considered. However, as high image quality in printers has spread in recent years, there has been a demand for further improvement of image quality by the appropriate correction of paper feed error in printers that perform printing in an interlace recording mode. This demand has been increased not only against interlace recording mode printers but also against non-interlace recording mode printers.
An object of the present invention is to provide a technique for improving image quality by correcting the paper feed error in a printer.
In order to attain the above object, the present invention executes prescribed processing in printing using a printing apparatus for printing by recording ink dots on a printing medium while moving a printing head in a main scanning direction. This printing apparatus comprises: a printing head including a plurality of nozzles arranged in a sub-scanning direction substantially perpendicular to a main scanning direction; a main scan drive unit configured to move the printing head in the main scanning direction, a sub-scan drive unit configured to move the printing medium in the sub-scanning direction by a plurality of intermittent feedings, a head driving unit configured to eject ink droplets from the nozzles while the main scan of the printing head, and a control unit configured to control the main scan drive unit, the sub-scan drive unit and the head driving unit.
With such the printing apparatus, a test pattern is formed on a printing medium. The test pattern includes a plurality of color patches printed in a plurality of printing modes, respectively. The test pattern is formed for selecting a printing mode from among the plurality of printing modes which are different each other in a sub-scan feed amount and/or an adjustment value for a sub-scan feed amount. Dots are recorded in accordance with a printing mode selected based on printing result of the test pattern.
With such an embodiment, image quality is improved by selecting the paper feed properly. This technique is described in many kinds of embodiment underneath.
(1) Pattern Printing in Interlace Printing Mode:
One embodiment for attaining the above object is as follows. That is a method for correcting the amount of sub-scan feed of the printing medium in a printing device which uses a print head that has a plurality of nozzles aligned in a row in the sub-scan direction, which is approximately perpendicular to the main scan direction, at a nozzle pitch of k times (k is an integer of 2 or greater) the dot pitch in the sub-scan direction, and which records ink dots on the printing medium while causing the print head to move in the main scan direction. The method comprises the steps of (a) printing, in accordance with an interlace recording mode, a test pattern that includes a plurality of color patches respectively printed using different correction values, as a test pattern for the purpose of determining the correction value of the sub-scan feed amount of the printing medium; and (b) correcting the sub-scan feed amount according to a correction value set in accordance with the printing results of the test pattern when the printing of images is performed in the interlace recording mode.
In this method, a test pattern that includes a plurality of color patches that are respectively printed using different correction values is printed according to the interlace recording mode, and the sub-scan feed amount is corrected using a correction value in accordance with the printing results of this test pattern. Accordingly, the sub-scan feed error of the printer that performs printing in an interlace recording mode can be corrected, so that the image quality is improved.
The step (a) may comprise the steps of as follows. These are (i) selecting N nozzles (N is an integer of 2 or greater) for each color among the plurality of nozzles as used nozzles; (ii) performing (k xe2x88x921) scan sets each comprising a single main scan and a sub-scan feed by a first feed amount that is equal to the dot pitch in the sub-scanning direction, and then further performing a single main scan and a sub-scan feed by a second feed amount which is equal to {Nxc3x97kxe2x88x92(kxe2x88x921)} time the dot pitch; and (iii) printing the test pattern by repeatedly performing the step (ii).
In the test pattern that is printed by such a printing method, band-form areas of image deterioration called xe2x80x9cbandingxe2x80x9d tend to be generated as a result of sub-scan feed error. Accordingly, if the correction value is determined using such a test pattern, the sub-scan feed error can be corrected so that banding tends not to occur.
It is preferable that the plurality of color patches are gray patches that are reproduced by composite black.
Composite black is reproduced using inks of the three hues CMY. The sub-scan feed error can be corrected with the ink dot trajectory error also taken into account; as a result, the mage quality can be further improved.
The plurality of color patches may be monochromatic patches that are reproduced using one ink among inks of black, cyan and magenta. The plurality of color patches may also be color patches of a secondary color that is reproduced using two inks among inks of three colors of cyan, magenta and yellow.
If inks with color components for which improvement of the image quality is especially desired are selected as the inks used to reproduce the color patches, the effect of the correction of the sub-scan feed error in improving the image quality is conspicuous.
(2) Pattern Printing in Given Ink Duty:
One embodiment for attaining the above object is as follows. That is a method for correcting sub-scan feed amount of a printing medium in a printing device that prints by recording dots onto a printing medium while moving a print head in the main scanning direction. The method comprises the step of (a) printing a test pattern for deciding a correction value for the sub-scan feed amount of the printing medium. The test pattern includes a multiplicity of color patches each printed at a different correction value, and being printed with one type of ink at ink duty of less than 100%. The method also comprises the step of (b) during printing, correcting the sub-scan feed amount in accordance with a correction value set with reference to the printed result of the test pattern.
With this method, color patches are printed using one type of ink at an ink duty of less than 100%, so that color patches that make image degradation due to paper feed error readily apparent can be printed. As a result, printer sub-scan feed error can be corrected with an appropriate correction value, and quality improved thereby.
The ink duty may be varied depending on a type of the printing medium.
Typically, if ink duty is excessively large, the ink tends to bleed, whereas conversely if it is too low, there is a tendency for image degradation due to paper feed error to become less readily apparent. It is normal for the susceptibility to ink bleeding to vary with the type of printing medium (particularly its surface qualities). Thus, by varying the ink duty depending on the type of printing medium, it becomes possible to print test patterns suitable for printing media of various kinds.
The plurality of color patches may be gray patches reproduced by means of black ink. The ink duty of each of the gray patches may be a value in a range of about 70% to about 90%.
With this embodiment, it is possible to print the test pattern that is suitable for deciding the proper correction value of paper feed error.
The plurality of color patches may be arrayed in a row in the sub-scanning direction on a single sheet of printing medium.
This embodiment allows a large number of color patches to be printed on a single sheet of printing medium, printing medium can be saved.
The print head may comprise a color nozzle row wherein a plurality of color nozzle groups are arranged in predetermined order in the sub-scanning direction, and a black nozzle row arranged juxtaposed to the color nozzle row. In such arrangement, it is preferable that the plurality of color patches are printed using only some of a plurality of black nozzles included in the black nozzle row.
With this arrangement, gaps between color patches can be made relatively small, allowing a large number of color patches to be printed on a single sheet of printing medium.
Furthermore, the present invention may be realized in various aspects; such as a method and apparatus for correcting the sub-scan feed amount (paper feed amount), a controlling method and apparatus for controlling the sub-scan feed, a printing method and apparatus which give consideration to the correction of the sub-scan feed amount, a printing control apparatus and method which are used to control a printing apparatus with consideration given to the correction of the sub-scan feed amount, computer programs for realizing such methods and apparatus, recording media for recording such computer programs, and data signals realized in carrier waves including such computer programs.
(3) Pattern Printing with Selection of Feeding Amount:
In order to attain at least part of the above objects, in one embodiment of the invention, the present invention executes prescribed processing with a printing device which performs printing by recording ink dots on a printing medium while causing a print head to move in the main scan direction. This printing device comprises: a nozzle group for ejecting drops of ink, a main scan drive unit for performing main scan by moving the nozzle group and/or the printing medium, a sub-scan drive unit for performing sub-scanning by moving the nozzle group and/or the printing medium in a direction intersecting the main scanning direction, an input unit for receiving data input from the outside, and a control unit for controlling each the unit.
With such printing device, color patches are formed on the printing medium using a multiplicity of dot recording modes in which the sub-scanning conducted at intervals between the main scans differs in content. Then a dot recording mode is decided by means of selecting one color patch from among the test patches. With this arrangement, a dot recording mode that gives the printed result of the best quality can be selected on the basis of actual printed results.
In case that the printing modes involves recording a plurality of pixels on a single main scan line over a plurality of different main scans, it is preferable that the color patches are formed on the printing medium using the plurality of dot recording modes in which the number of main scans needed to record all pixels on a single main scan line is mutually equal, and in which the sub-scan feed content conducted at intervals between the main scans is mutually different. With this arrangement, a dot recording mode can be selected from among a plurality of dot recording modes in which the number of the main scans needed to record all pixels included in a single main scan line are mutually equal. The selection can be made based on the quality of printed results that differs because of the differences of orders of recording pixels of a single given main scan line or the differences of the combinations of nozzles used to record each pixel.
It is preferable that the plurality of dot recording modes employ different combinations of nozzles for recording a plurality of pixels that are contiguous in the sub-scanning direction. With this arrangement, dot recording mode can be selected from among a multiplicity of dot recording modes that give printed results of different quality.
In forming color patches, the color patches may be formed on the printing medium using the plurality of dot recording modes each of which involves repeated execution of the sub-scan by a single constant feed amount. The dot recording modes may mutually differ in the feed amounts. In such the case, it is preferable that the feed amounts in the plurality of dot recording modes of mutually different feed amounts are substantially equal. With this arrangement, printing speed does not vary significantly regardless of the dot recording mode selected.
In forming color patches, it is preferable that color patches are formed on the printing medium using the plurality of dot recording modes each involving repeated execution of a unit sub-scan. In this arrangement, the unit sub-scan may include sub-scans with a plurality of feed amounts, and the dot recording modes may differ in an order of execution of sub-scans with the plurality of feed amounts included in the unit sub-scan, and/or in the plurality of feed amounts. In such an arrangement, the plurality of dot recording modes for repeated execution of the unit sub-scan have substantially equal average values for feed amount of the sub-scans included in the unit sub-scan. With this arrangement, printing speed does not vary significantly regardless of the dot recording mode selected.
In forming color patches, it is preferable that the color patches may be formed by forming dots with magenta, cyan and yellow inks in each of the dot recording modes. With this arrangement, it is possible to produce test patches that readily reflect image quality of printed results in color printing.
The present invention may be implemented to practice in number of embodiments, such as the following.
(1) Method for deciding dot recording mode; printing method; printing control method.
(2) Printing device; printing control device.
(3) Method for producing printing device.
(4) Computer program for implementing the device or method.
(5) Storage medium having recorded a computer program for implementing the device or method.
(6) Data signal including a computer program for implementing the device or method, and embodied in a carrier wave.